• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 639 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

HDC2010: one question for HDC2010

Oliver Ou
Intellectual 2845 points
Part Number: HDC2010

Hi Team,

Customer has an application issue for HDC2010, could you help checking and give some suggestions?

In our design, due to the heating from the inner, the hdc2010’s temperature will be 1.4℃ higher than outside air temperature. Will the RH% will be affected by the temperature. If yes, how much it will be? Is there a formula regarding humidity error caused by temperature deviation.

Thanks.

Oliver Ou

  • 0
    TI__Mastermind 28075 points

    Hi Oliver,

    Thank you for your question. The HDC2010 senses relative humidity (RH) directly, so the temperature reading being high or low does not affect the accuracy of the RH results. It is true that heating the sensor can dry out the polymer, which is the way the heater works, but 1.4C is not enough to noticeably affect the HDC2010 in this way. 

    With that in mind you shouldn't need to apply any correction to the RH readings. 

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 90 points

    Hi Brandon

        Sorry for taking so long to reply this issue. Oliver is our FAE. He suggestd we continue the discussion in here. 

        Thank for your answer. But I want to share a test result of humidity of our product. We test 3 samples and a standard meter in chamber, and the temperature is contant but humidity varies. Based on the result, The greater the environment humidity, the greater the deviations. At point 70%RH, 2 samples' deviation is over 3%.

        As mentions the temperature around the hdc2010 in box will be 1.4℃ higher than the real temperature outside. So we think it maybe also the cause of deviation.   

        Formula for humidity:          Humidity = ( Water vapor amount / saturated water vapor amount ) *100 (rh%)

        So the hdc2010 temperature is higher than the real world. So the saturated water vapor amount will also higher. So the humidty will lower than the real world, right?  

  • 0 in reply to Jason Tu
    TI__Mastermind 28075 points

    Hi Jason,

    Thanks for following up. 

    I'm not sure what was shared with you via email, but my initial post was incorrect. In your case you DO need to apply an RH correction based on the temperature difference. The RH sensor will still return the correct value for the region where the air is 1.4C higher (inside your case), but since you want ambient RH you will need to compensate for the difference in temp. 

    You should be able to apply a correction based on the ratio of Saturation Vapor Pressures:

    ­­Where:

    • RH1 is the initial RH Reading
    • RH2 is the corrected RH Reading
    • PWS1(T1) is the saturation vapor pressure at the sensor read temperature (T1)
    • PWS2(T2) is the saturation vapor pressure at the corrected temperature (T2)

    You can use a look up table for saturation vapor pressures, or you can calculate it with the August-Roche-Magnus formula:

    Which is useful from 0 °C to 100 °C.

    As you've noted, this correction would result in an increase in humidity, since PWS1 is greater than PWS2. It seems to me that you have a positive offset in your humidity reading. Here's a couple things that may be the source.

    • What is the guaranteed accuracy of your reference? Is it properly calibrated? 
    • Has the sensor been exposed to any chemicals that are listed here?
    • Did you wash the boards with the device on it, or have the devices potentially been exposed to condensation? If so, attempt a bake of the boards (100 °C for 6-10 hours is typically enough), and reassess the accuracy.

    Best Regards,
    Brandon Fisher